Low Oxygen Cause of Menhaden Die-off in Delaware Bay

Aug 13, 2010

The New Jersey Department of Environmental Protection (DEP) on Aug. 12 received new water sampling results that strongly suggest low oxygen levels were behind the massive die-off of menhaden in Delaware Bay.

Three of four samples taken showed dissolved oxygen levels below 5 micrograms per liter. Any level below that is considered biologically stressed. The fourth sample was just above the threshold.The lowest reading - 3.4 micrograms per liter - was recorded at Pierce's Point in Middle Township, one of the areas hard hit by washed-up fish.

"Although taken after the fact, these tests suggest that oxygen levels in the bay were probably very low and caused the die-off of fish," said Robert Van Fossen, the DEP's assistant director for Emergency Management. "These low levels likely occurred as a result of very warm weather and warm temperatures in the bay. The warmer water is the less dissolved oxygen it is able to hold. If the fish schooled very tightly in shallows very close to shore for any reason, they may have simply used up all the oxygen that was available to them and died."

Meanwhile, the DEP has given local governments approval to use heavy equipment to remove the fish from the beaches. While many of the decaying fish appear are being carried back into the bay by tides, many more will need to be collected and disposed.

"Given the extraordinary circumstances, we took swift action to provide municipal and county officials clear direction on how to address this situation," said Wolf Skacel, DEP's assistant commissioner for Compliance and Enforcement. "All we're asking is that they try to restore the sand on the beaches to as close to natural as possible when they are done."

Removal operations are expected to begin today. The focus of the cleanup will be in the most heavily impacted area, an eight-mile stretch of shoreline from Bidwell Creek south to Shadeland Avenue in the Villas section of Lower Township. The fish will be taken to the Cape May County Landfill in Woodbine.